The present invention generally relates to presses capable of bending plate material or the like. In particular, the present invention is directed to a rugged and dependable adjustable die assembly including a pair of die members capable of being easily, quickly and accurately positioned relative to one another to allow for selective bending of a workpiece at a variety of predetermined angles and/or radii.
Large capacity hydraulic or mechanical presses e.g. of about 500 tons and larger capacity, have suffered from long standing problems preventing quick and accurate adjustment of the die members relative to one another. Because components of the forces generated in such large capacity machine assemblies during the bending of relatively thick steel plate must pass directly through the die members, it has long been considered necessary to employ die members having considerable mass. However, the very mass necessary for withstanding such forces makes it exceedingly difficult to move the die members relative to one another when adjusting the gap between the die members for changing the angle of bend to be formed in the workpiece. Moreover, certain of the temporary fastening or positioning means for the dies which are sufficiently rugged to withstand the aforementioned forces suffer from limitations in respect to versatility and ease of adjustment, while other more versatile and readily adjustable fastening or positioning means suffer from disadvantages of complexity, costliness and inadequate ruggedness. Moreover, if the dies are mounted in a frame which is not integral with the press bed and secured to a keyway therein, difficulties have been encountered in effecting proper alignment of the frame with the bed and consequently with the ram of the press.
A known arrangement providing considerable ruggedness and accurate die positioning involves bolting the dies to the inner surfaces of upright sides of an open-top (often also open-ended) rigid box or cage. To adjust the die spacing, the dies are unbolted, shims of predetermined thickness are inserted between their back sides and the sides of the box or cage and the dies and shims are then bolted into the box. However, a relatively large number of pairs of shims of various sizes must be employed to provide a wide variety of required bending angles. Because each pair of shims is relatively expensive and must be stored when not in use, this arrangement suffers from disadvantages of cost and storage requirements. More importantly, shims employed in heavy duty press brake assemblies can themselves be exceedingly heavy and cumbersome, often requiring two or more employees just for lifting and positioning the shims. It becomes evident that while shims may vary the gap between die members, shims do not provide a quick, inexpensive and simple way of adjusting the die members.
In attempts to eliminate the above disadvantages, some presses have been fitted with elaborate carriage mechanisms for moving the die members. However, because such carriage mechanisms are often complex in nature, they are costly and subject to mechanical breakdowns. That they have not fully met existing needs is evidenced by the continuing widespread use of the cumbersome box and shim arrangements described above.
When adjustable dies are mounted on (including in) a box-like or other type of frame, it is then usually possible to remove them from the press in order that other types of tooling can be used therein. To provide a means for proper alignment of the frame and dies with the elongated ram of the press during reinstallation of the dies, a keyway is frequently provided in the press bed beneath the ram, in which is received a key or keys of corresponding width keyed into or integral with the die set on the centerline of the underside of the frame. Past experience with removeable frame die sets has disclosed a harmful tendency for the ram to cock toward one side or another as it presses down on the workpiece. In the course of an extended search for the difficulty it was learned, surprisingly, that in the present state of the art of manufacturing large capacity presses it is extremely difficult to achieve accurate alignment of such keyways with the plane in which the longitudinal axis of the ram face moves up and down in the press. Accurate alignment has not been achieved in relatively large numbers of the presses in use today. Thus, in such presses, an adjustable die set which is accurately aligned with the bed keyway will be off-center relative to the ram. In such circumstances the ram will contact the work off-center, and as the work bends it will exert side-wise forces on the ram which cause the cocking action referred to above.
As will become apparent from a reading of the following description and claims, the present invention provides a uniquely constructed adjustable die assembly which overcomes known problems confronting prior art assemblies as discussed hereabove. In particular, the present invention provides a pair of die members capable of being quickly and accurately adjusted relative to the press ram and to one another without the need for any cumbersome shims or costly carriage mechanisms or the like, while resisting force components generated in presses having capacities of up to 500 tons and higher.